Gasification systems may be used in various applications, including chemical production systems and power systems. For example, combined cycle power systems generally may include a gasification system that is integrated with a gas turbine engine and other components to produce power. The gasification system may include a gasifier configured to receive a mixture of fuel, air/oxygen, steam, and possibly other materials therein to produce a partially oxidized gas known as “syngas.” The resulting syngas ultimately may be directed to other components of the combined cycle power system, such as a combustor of the gas turbine engine, for combustion therein.
The gasification system also may include a feed injector configured to atomize and mix the fuel, air/oxygen, steam, and other possible materials, and to deliver the mixture to a reaction zone of the gasifier. During operation, the feed injector may be exposed to temperature extremes within the gasifier. Specifically, a tip of the feed injector, which may extend into the reaction zone of the gasifier, may be exposed to gasification reaction temperatures of up to about 2600° F. (1427° C.). Such high temperatures may inhibit effective operation of the feed injector and may shorten the life span of the feed injector tip. Further, the feed injector may be exposed to corrosive elements carried in the syngas produced within the gasifier, resulting in an effect known as “sulfur attack.” Over time, such corrosion also may inhibit effective operation of the feed injector and may shorten the life span of the feed injector tip.
In order to protect the feed injector from the adverse effects of high reaction temperatures, certain gasification systems may include a closed-loop water cooling system to provide cooling water to the feed injector tip. The closed-loop water cooling system, however, may be complex to manufacture and costly to operate. Further, use of the cooling system may produce areas of localized strain and may result in cracking of the feed injector tip. Specifically, the metal temperatures between an internal air/oxygen passage and an internal cooling water passage about the feed injector tip may be relatively low compared to the metal temperatures along an outer surface of the feed injector tip exposed to the reaction zone. For example, the temperature difference may be a multiple of about ten (10) times or so. The stiffness of the metal may decrease as the temperature increases, and thus the metal along the hotter outer surface may elongate more than the metal along the cooler inner surface, resulting in an area of high thermal strain and stress therebetween. Over time, this area of high thermal strain and stress may result in cracking of the feed injector tip or other damage thereto. Such cracking also may be facilitated by mechanical stress due to a pressure difference across the feed injector tip. Ultimately, cracking of the feed injector tip may allow the syngas to penetrate into the cooling water passage and contaminate the water therein, requiring costly and time-consuming shutdown of the gasification system and replacement of the feed injector.
Certain feed injectors may include a number of bayonet-style tubes arranged in a concentric manner and defining a number of concentric feed passages therethrough. For example, a feed injector may include three tubes, an outer tube, an intermediate tube, and an inner tube, which define an outer feed passage, an intermediate feed passage, and an inner feed passage, respectively. According to certain arrangements, the outer and inner feed passages each may deliver a flow of air/oxygen, and the intermediate feed passage may deliver a flow of fuel, such as oil, gas, or coal slurry. In this manner, the tubes may be subjected to high pressures and high velocities of the flows of air/oxygen passed therethrough, which may inhibit effective operation of the tubes and may shorten the life span of the tubes. Moreover, when the flow of fuel is coal slurry, the tubes may be impinged upon by coal particles traveling at high velocities, resulting in an effect known as “slurry erosion.” Such erosion may be particularly significant at the tips of the tubes, increasing the tip openings over time and thus decreasing the flow velocity of the coal slurry and the overall performance of the feed injector.
According to certain bayonet-style feed injectors, each of the tubes may include a pipe portion and a tip portion fastened to one another, for example, by welding. In this manner, the tip portion may be replaced periodically due to cracking, corrosion, or erosion that may occur as discussed above. However, replacement of the tip portion may require costly and time-consuming shutdown of the gasification system and may be particularly complex when the gasification system includes a cooling system connected to the tip portion, for example, by welding. Moreover, the cost of replacement tip portions may be significant due to the expensive materials required to even temporarily tolerate the high temperatures, pressures, and velocities experienced during operation of the gasification system.
There is thus a desire for an improved feed injector configured to deliver a mixture of fuel, air/oxygen, and steam to a gasifier of a gasification system. Specifically, such a feed injector should address the risks of cracking, corrosion, and erosion of the feed injector tip to increase the life span of the feed injector, while providing acceptable operability at the high temperatures, pressures, and velocities experienced during operation of the gasification system. Moreover, such a feed injector should reduce the complexity and cost of manufacturing and operating the feed injector. Further, such a feed injector should reduce the frequency and duration of replacement thereof and thus should reduce costly shutdown of the gasification system and the overall system in which it is used, such as a combined cycle power system.